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Welding grossly dissimilar thicknesses

03-26-2012, 02:04 PM

Hi,
Yet another newbie here; not just to this site, but to MIG welding as well.

For those who are pretty experienced, I suppose welding a solid 1/2" round bar
through a 16 gauge tube at a right angle is no big deal. For me, and doubtless many others, its a pain to weld hot enough to cut into the round bar without blowing holes in the light gauge tubing.

I haven't tried this, but I'm wondering...What if you were to put say an inch or so of #8 or 9 steel shot on the inside of the tubing so it packed around the 1/2 inch bar prior to welding? Wouldn't this work to effectively increase the mass of the thin tubing?

I remember in my early stick welding days chasing a pinhole in a Harley gas tank for about six inches before I gave up and bought my buddy a new tank!

I don't think spherical shot is going to contact the tube enough to draw the heat out. I think you'd still be heating the entire thickness of the tube up to melting point. You'll probably achieve welding some of the shot to the inside of the tube.

In this case you'll need to try to put the heat onto the larger piece and just enough onto the thin tubing to get the weld well attached.

Remember there's no benefit to putting a larger weld than your smallest piece. If it's over stressed, a large weld on a 16ga tube is just going to result in ripping a hole in the tube around the outside of the weld. The larger weld doesn't make it any stronger. Keep the weld sized small to match the tube thickness. This will help keep the heat down and help your burn through problems.

Comment

Filling the tube with water might help a bit. From my old days of Oxy-Acetylene welding and trying to get some heat into a pipeline filled with water it was a SOB!
In reality, you just need to concentrate the heat on the thick stuff first and whip it on and off the thin stuff.

Comment

If using a mig welder i will set up the machine to run a litlle less hot than required for the thinest gauge so you can run slower on thick, faster on thiner tube ,weld will be amazing, there are many tricks out there ; thats the one i use with good results,litlle dificult to control but works without perforating or deforming your material

Comment

Most applications of gas metal arc welding use a constant voltage power supply. As a result, any change in arc length results in a large change in heat input and current. A shorter arc length will cause a much greater heat input, which will make the wire electrode melt more quickly and thereby restore the original arc length.

Comment

If I was doing it I'd concentrate my heat on the solid round bar washing down over the 16 ga. If you're not comfortable doing that you might try a series of tacks spaced 180 degrees apart until the weld bead is complete. Clip the scab off the end of your wire before the start of every tack.

Comment

turn the voltage down to about 15 or 16, start your puddle at the thicker metal then bring it back up to the thinner metal in your case the tubing. Weld for a couple of seconds until you see your whole bead turn bright orange, then let the metal cool down! maybe go to the other side and start there when one side is cooling down. i had to do this when i was patiching up some holes i had in my hot water heater that i was turning into a calf grain bin